S.L. 427.4 Art. 2of at least 20 ASTM E 92-65 (Revision determinations.

PHYSICAL DETERMINATIONS

2.1 Density Method by hydrostatic balance to within ± 0.01. A sample grams is weighed in air and weighed immersed in distilled water at 20ºC. 2.2 Refractive index The index is measured on the refractometer to within ± 0.001.

2.3 Microhardness Vickers hardness is to be measured according to the standard 1965) but using a load of 50 grams and taking an average of 15